Ethylenediamine tetraacetic acid (EDTA) and 1,10-phenanthrorine (phen) were covalently attached to the 5' and 3' ends of two different oligonucleotides (ODNs), respectively. The sequences of the ODN conjugates were designed to contiguously hybridize on the target DNA with their auxiliary units facing each other, providing a microenvironment to accommodate the lanthanide ions. The characteristic emissions of the Tb3+ and Eu3+ ions were clearly observed in the presence of the full-matched target DNA. On the other hand, the emissions from the mixed solutions with the mutant containing one base displacement were marginal.